Income Taxes (Unrecognized tax benefits) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns, Net [Roll Forward]    
Balance at January 1 $ 7 $ 5
Additions for tax positions of prior years 0 2
Balance at December 31 $ 7 $ 7